Engine combustion using diesel or gasoline fuel may generate particulate matter (PM) (such as soot and aerosols) that can be exhausted to the atmosphere. To enable emissions compliance, particulate filters such as diesel particulate filters (DPFs) and gasoline particulate filters (GPFs) may be included inline in the engine exhaust stream, to filter out exhaust PMs before releasing the exhaust. Particulate filters that become clogged with PM may be regenerated in-situ during deceleration fuel shut off (DFSO) events by supplying excess oxygen to the filter and raising the filter temperature to oxidize the PM. One example approach shown by Bidner et. al. in U.S. Pat. No. 8,424,295 discloses increasing excess oxygen to the particulate filter during engine shutdown conditions and regenerating the particulate filter at least during a portion of the engine shutdown.
However, the inventors herein have recognized potential disadvantages with the above approach. Oxygen flow to the filter during DFSO or other engine shutdown events may increase the filter temperature excessively leading to premature filter degradation. Furthermore, employing strategies to limit DFSO duration to mitigate excessive exhaust particulate filter temperature increases and premature filter degradation can reduce fuel economy, and may also reduce drivability. Further still during short engine on periods (e.g., during short vehicle trips), the particulate filter temperature may fail to reach a high enough temperature for regeneration.
The inventors herein have identified an approach that at least partly addresses the above issues. In one example, a method for a combustion engine may comprise: during a cold start condition comprising an engine temperature being less than a threshold engine temperature, directing engine exhaust gas to an exhaust particulate filter; and during a warm engine condition, directing engine exhaust gas to bypass the exhaust particulate filter, wherein the warm engine condition comprises the engine temperature being greater than or equal to the threshold engine temperature and fuel being combusted in the engine.
In another example, a method may comprise: in response to an engine temperature being greater than a threshold engine temperature, directing exhaust gas to bypass an exhaust particulate filter during engine fuel combustion, and heating the exhaust particulate filter when an exhaust particulate filter temperature decreases below a threshold filter temperature; and in response to an engine temperature being less than a threshold engine temperature, directing exhaust gas to the exhaust particulate filter and ceasing to heat the exhaust particulate filter.
In a further example, an engine system may comprise: an engine; an exhaust particulate filter positioned in an exhaust bypass passage downstream of the engine; an exhaust diverter valve positioned upstream of the exhaust bypass passage; and a controller, including executable instructions to, during a first condition comprising an engine temperature being less than a threshold engine temperature, positioning the exhaust diverter valve to direct engine exhaust gas to the exhaust bypass passage and the exhaust particulate filter; and during a second condition, positioning the exhaust diverter valve to direct engine exhaust gas to bypass the exhaust bypass passage, wherein the second condition comprises the engine temperature being greater than or equal to the threshold engine temperature and fuel being combusted in the engine.
In this way, the technical effect may be achieved that the exhaust particulate filter may be reliably regenerated during engine shutdown events such as DFSOs without premature degradation. Furthermore, by avoiding any limiting of the engine shutdown events, drivability and fuel economy are maintained. Further still, by diverting the exhaust stream to the exhaust particulate filter during engine cold start conditions and bypassing the exhaust particulate filter during warm engine combustion conditions, the exhaust particulate filter size may be reduced thereby lowering manufacturing costs and improving reliability while maintaining vehicle PM emissions. Further still, by heating the exhaust particulate filter during warm engine conditions and during engine fuel combustion, the exhaust particulate filter temperature can be preheated to a temperature high enough for filter regeneration.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.